This application relates to methods for leak-testing a fuel supply system, wherein the fuel supply system comprises a fuel tank, a fuel injection valve, fuel lines between the fuel tank and the fuel valve, and a control valve controlled by a diaphragm, wherein the diaphragm bounds a control chamber on one side, wherein the control chamber is filled with fuel, and wherein the control valve closes when the pressure in the control chamber rises above a predetermined pressure, the method comprising:
acting upon the portion of the fuel supply system upstream of the control valve with a predetermined pressure level,
acting upon the side of the diaphragm facing away from the control chamber with a counterforce, wherein the counterforce is equal to or greater than the predetermined pressure level.
This application also relates to a device for leak-testing a fuel system, wherein the device comprises a test pressure unit with at least one test pressure line, wherein said test pressure line is connectable to the fuel supply system. Handheld tools, such as motorized chain saws, trimmers, abrasive cutting-off machines or the like frequently have an internal combustion engine, in particular a two-stroke engine, as the driving mechanism. In order to supply the internal combustion engine with fuel, use is made of a fuel tank and a fuel line, which may comprise a plurality of sections, and a control valve. The control valve is actuated depending on the fuel pressure in a control chamber, wherein the fuel pressure in the control chamber acts on a diaphragm, the deflection of which moves a valve closing member relative to a valve seat via kinematics. Such a construction of a control valve in a fuel supply system has been tried and tested and is used both in the case of internal combustion engines having a carburetor and also in the case of those having fuel injection. In such a control valve, the diaphragm takes up different positions depending on the forces acting thereon, namely a first position, in which the control valve is completely open, a second position, in which the control valve is closed, and third positions which are located between said positions and in which the control valve is partially open.
Within the scope of production of a tool mentioned above, provision is made for the fuel supply system to be subjected to a pressure test in order to ensure the tightness of all of the fuel guiding elements. Use is made for this purpose of a test pressure which is a multiple of the operating pressure of the fuel system, for example is a multiple of 8 to 10 times. In the case of fuel systems having low pressure injection of the fuel into the engine, the pressure between a fuel pump and the injection valve is approximately 100 mbar, and the control valve is set for said pressure level. This is a problem for the pressure testing of the fuel lines and components arranged downstream of the control valve, because the respective fuel supply system sections located upstream of the control valve and downstream of the control valve have to be subjected to separate pressure tests.